Males with the largest testes, most fit sperm and longest endurance in the sack tended sired more offspring with promiscuous females

On the list of most desirable ways to kick the bucket, expiring in a blaze of passionate exertion ranks near the top. Males of several marsupial species have evolved to do just that. Their brief existence revolves around preparing for sex and culminates in that final act. While this strategy of “sexual suicide” is often employed by insects, in mammals, LiveScience points out, it’s rare.

Most animals that pursue this tactic, like squid and spiders, have many offspring, making it more understandable from an evolutionary point of view: Though they die after mating, they likely have thousands offspring to which they pass on their genes, Fisher told LiveScience. But marsupials, like most mammals, only have a few offspring at a time.

Fisher explains that males employ this strategy because it maximizes their chances of siring healthy, strong pups. The New Scientist writes:

Rather than growing fighting-fit bodies, the males pour everything they have into fighting-fit sperm. This leaves them with nothing in reserve to fend off disease afterwards.

Just prior to mating, the males’ massive testicles stop producing sperm and even begin to break down, LiveScience explains, ensuring that they can put all of their energy into the act of transferring that sperm to as many females as possible. But that also creates a limited window for males to get rid of all of that sperm. Once game time arrives, some species are known to mate up to 14 hours straight, LiveScience writes. During that time, males’ muscles may begin to break down to lend them an extra energetic boost. ”The have a frenzied mating season lasting only a couple of weeks, and males usually die before young are born,” Fisher told LiveScience.

In those species that have completely adopted the shorter mating system, all males die: Elevated stress levels cause a fatal immune system collapse and death by hemorrhaging and infection.

The strategy does work. The males with the largest testes, most fit sperm and longest endurance in the sack tended sired more offspring with promiscuous females than their less fecund competitors, Fisher told National Geographic.

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